Lyme disease, due to infection with the Ixodes tick-transmitted spirochete Borrelia burgdorferi, is the most common vector-borne disease in the United States, with more than 28,000 cases reported annually. The infection can remain localized to the skin or disseminate to cause disease in the skin, heart, joints and nervous system. The ospC genotype of the spirochete may determine its invasiveness and propensity to disseminate. Although antibiotics achieve clinical cure when administered in early stages of infection, disseminated infection or delay in diagnosis can lead to substantial morbidity and health care expenditures. Timely and accurate diagnosis of Lyme disease is essential for optimizing treatment and for preventing long-term sequelae of the disease. Because few spirochetes are found in infected tissues, the host immune response provides the basis for most commercial laboratory tests that support a diagnosis of Lyme disease. Serologic tests (ELISA and immunoblot) that detect B. burgdorferi-reactive antibodies are the most widely used tests, but have lower sensitivity and specificity in early infection and can be indeterminate in later stages, particularly if antibiotics have been administered. In addition, current Lyme serologic tests do not distinguish previous exposure to B. burgdorferi from active infection, and no serologic test to date can be used to assess response to therapy. This Phase 1 proposal seeks to improve upon the currently available Lyme diagnostic tests by evaluating the feasibility of a novel T cell cytokine assay using whole blood for the diagnosis of disseminated B. burgdorferi infection and for monitoring response to therapy. The key to our approach is the use of two unique B. burgdorferi proteins required for establishment of infection (OspC) and persistence (VlsE) as antigenic stimuli for cytokine induction. Recombinant forms of OspC and VlsE will be produced and T cell cytokine profiles mapped after tick-borne infection in mice over a period encompassing localized infection, dissemination and persistence. Antigens will be optimized for detection of signature cytokine responses elicited by B. burgdorferi infection with 5 strains representing the main ospC genotypes associated with dissemination (genotypes A, B, I, K, and N). Assays with optimized antigens will be used to assess whether the rate of decline of signature cytokines predicts antibiotic elimination of infection in mice. Finally, pilot studies will be performed to assess the specificity of the response using blood samples from subjects with and without Lyme disease. The results of this Phase 1 study will set the stage for the development of new rapid and specific cellular immune assays for Lyme disease that complement current and future serologic tests to enhance early diagnosis and to monitor response to therapy. PUBLIC HEALTH RELEVANCE: Lyme disease, due to infection with the tick-borne spirochete Borrelia burgdorferi, is the most common vector-borne disease in the United States. Timely diagnosis of infection is important for optimal response to therapy and to prevent long-term sequelae. This project will assess the utility of a T cell cytokine assay for the detection of disseminated B. burgdorferi infection and for monitoring efficacy of treatment.